UR Force mode using values from an external sensor

Erik 2017-03-20

Hi all,

The UR Force mode in Polyscope is not enough accurate for some applications because the calculated forces at the TCP (based on the joints currents) are not accurate.
From Polyscope 3.3, it's possible to develop an URCap where an external force/torque sensor feeds its measurements directly into the UR force control loop.

Does anyone know if an URCap based on the FT300 has been already developed somewhere?

Thanks.

Erik
SYSAXES

Annick_Mottard 2017-03-16

Hi @Erik

It is possible to feed the FT300 output in the UR force mode. This post sums it. You need to use RTDE in order to do so. As of today, the FT Sensor URCap does not include the functionality of streaming the sensor data in the UR force mode.

Erik 2017-03-16

Hi Annick,

Thank you very much for your quick answer. In the other post, Samuel says it's has to be in your URCaps, do you know when it will be done?
One of our automotive customer needs it asap.

Thanks.
Erik

matthewd92 2017-03-16

@Erik it doesn't have to be in the URCap, you could monitor the forces from the FTS externally and then feed them into the controller from a second computer using RTDE running a script on that computer. Depending on how savvy you are with programming there are some example programs in python on UR's support site here that could be used to feed that data into the robot externally.

It will just be very nice when it is in the URCap as then it will be a simple plug and play kind of thing.

@Samuel_Bouchard this would be our primary use for a FT sensor in our applications, just getting better force feedback especially in the force node, any update on if this made the product roadmap you can share?

Nicolas_Lauzier 2017-03-27

@Erik, @matthewd92 I'm stepping in to add a few comments about the availability of this feature in our FT Sensor URCap.

In the past months, we made it work internally and ran a series of test in order to measure the effect of feeding the force signal into the UR controller. The improvement for realistic use cases (e.g. polishing) was negligible and during our tests we realized that although the FT signal is sent to the controller, the control algorithm of the robot is not changed. As such, it generally doesn't provide a better force control.

The only use case that was improved significantly was using the force mode towards a fixed point, for example if the robot is pushing against a part up to a given force. However, this is already possible using our current URCap (if you do a move inside of a "if" statement monitoring the force continuously).

Because the gains were not significant, we decided not to include this feature inside of our FT URCap. That being said, we are open to feedback from people who have used it with success.

heingab 2017-07-30

Hi, I'm currently trying to implement this on our system. I'm fairly new to the UR ecosystem so this may be a dumb question but I'm not seeing how to actually pipe the FT sensor readings into the system. I'm currently using the RTDE interface so I know the basics of how that works. But where do you actually override the internal FT estimates for use in force control mode?